Babies were less likely to get an itchy skin rash when their mothers took probiotics during pregnancy and while breastfeeding, in a new study from Finland.
Known as eczema, the rash is caused by an allergic reaction and hints at future problems with allergies and asthma.
Researchers said it's possible that probiotics - which are thought to help balance bacteria populations in the gut and prevent disease-causing strains from spreading - may influence babies' health through immune cells that cross the placenta and later are passed in breast milk.
Still, it's too early to send all pregnant women out to buy "good bacteria" supplements, some researchers said.
"While our results are promising, it is not yet possible to make recommendations for routine use of probiotics to reduce the risk of eczema," the study's lead author told Reuters Health in an email.
For the new study, Dr. Samuli Rautava of Turku University Central Hospital and his colleagues assigned 241 pregnant women to take one of two different probiotic combinations, given as a powder mixed with water once daily, or a bacteria-free placebo powder.
All of those mothers-to-be had a history of allergies, so their babies were at extra-high risk of eczema and other allergic reactions.
The women drank their assigned concoction for the last two months of pregnancy and their first two months of breastfeeding. Researchers then tracked their babies' health for two years to see how many developed rashes.
By the end of the study, 71 percent of babies in the placebo group had had eczema at least once, compared to 29 percent of babies whose mothers took either probiotic combination. Chronic eczema was diagnosed in 26 percent of placebo kids, compared to 10 percent and six percent, respectively, of those in the two probiotic groups.
However, by age two there was no difference in kids' sensitivities to a range of allergens, including milk, wheat, soy and dog and cat dander, based on whether their mothers had taken the supplements. About one-quarter of kids had a positive "skin prick" test for sensitivity to an allergen, the researchers reported last week in the Journal of Allergy and Clinical Immunology.
Dr. Ruchi Gupta, an allergy and eczema researcher at the Northwestern University Feinberg School of Medicine in Chicago, called the study "fascinating."
"It really shows a reduction in eczema from probiotics, which is such a simple and easy intervention for mothers," said Gupta, who wasn't involved in the research.
But she said it's too soon to tell if that reduction in eczema will also be tied to a drop in asthma and more serious allergies later on.
The probiotic strains used in the study were donated by Nestle, which markets probiotics in infant formula and other products.
Rautava and his colleagues didn't find any evidence of probiotic-related side effects. Stomach complaints, in particular, were just as common in mothers and kids in the placebo group as in the probiotic study arms.
The researcher said there have been reports of infections attributed to probiotics in babies, but that giving the supplements to mothers-to-be instead of to the babies themselves, as his team did, may reduce that risk.
Gupta thinks the side effects tied to probiotics have been so minimal that the supplements are worth taking for many people, especially pregnant and lactating women.
"We can safely advocate and encourage pregnant women of the potential advantages of taking probiotics," she told Reuters Health.
Probiotics, now sold by a range of companies to support immune and digestive health, run about 25 cents per day.
Some researchers have questioned whether the supplements sold on drugstore shelves have any real health benefit - especially given the number of different bacteria strains available, all with potentially different functions.
"The results look encouraging, but this is a controversial area and confirmation is needed," Dr. James Gern, a pediatric allergy researcher from the University of Wisconsin School of Medicine and Public Health in Madison, who wasn't involved in the new study, told Reuters Health in an email.
The U.S. Food and Drug Administration classifies probiotics as a food or dietary supplement. That means the products don't have to be proven to work before they're marketed, but they can't be billed to treat or prevent any specific disease.